1. Field of the Invention:
This invention related to improvements in attachment devices used to secure dental tools in dental hand pieces. The invention is more particularly concerned with, but not limited to, means for securing the dental tool within the dental bur tube, whereby part of the dental tool and part of the bur tube interlock so that the dental tool is unable to travel up or down the bur tube, but can be driven by the rotation of the bur tube.
2. Description of the Prior Art:
Many dental instruments incorporating cutting elements as well as sand-paper discs, abrasive wheels, etc., are driven by what is called a latch-type mandrel or bur tube arrangement. This incorporates a tool having a short longitudinal flat at the end of a shank, the shank also having a circumferential groove. Historically the tool or instrument has been driven by a rotating bur tube which has a chordal hole broached into the end to receive the flat of the bur shank for obtaining the rotational drive, and either a hinged latch or sliding latch operated from outside the end of the hand piece, to be slipped into the groove formed in the mandrel to engage the mandrel so that it does not come out of the handpiece.
The present invention has advantages over that type arrangement. It has no latch and so can have a smaller head of the handpiece, whence it is easier to reach the buccal or outside surfaces of the teeth with less distention of the cheek. It also eliminates the necessity of having openings in the back part of the instrument head where bacteria and saliva can enter the hand-piece, making it more aseptic. It eliminates use of the latch as the thrust bearing for the mandrel, and consequently eliminates a factor causing rapid wear and that creates a possible safety hazard, in that, once the latch wears sufficiently, the mandrel and/or dentral instrument can fall out of the handpiece. The present invention also eliminates use of a latch as a stationary member in the handpiece in which the mandrel rotates, and hence reduces heat and friction. It reduces end play that is due to the design of the latch-to-groove attachment that reduces efficiency and accuracy. And by eliminating a slotting operation, and a drilling and tapping operation to hold the screw for the latch, plus the latch and other parts, a reduction in cost is obtained.
The present invention can use the conventional bur or tool shank with the flat and groove, but drives by a fixed radially-inward projection that engages the flat after a short arcuate movement of the bur tube relative to the bur shank, such movement also causing the over-hanging flat lug of the bur tube to move into the groove under the flange of the bur shank to prevent the bur from coming out of the tube. Also a spring latch operates toward the same and releasably retains the bur shaft when the bur does not have the aforesaid arcuate displacement.
With this construction, the entire latch system is eliminated allowing the design of a much smaller head, the elimination of the mandrel rubbing the latch and elimination of the wear that occurs on the conventional latch mechanism and on the mandrel and/or instrument. There is also no intermediate tube between the dental tool and the bur tube as there are in devices known in the prior art.
Another embodiment of this invention is that the contra angle back end portion of this handpiece will allow the dentist to use not only the latch type head but the friction grip head and the triple seal prophylaxis head giving him complete flexibility and utility for the contra angle back end portion of the handpiece.
Further, the arrangement can be assembled from one end only of the handpiece head. The single restricted opening at the working end of this contra angle significantly lowers the area in which debris, saliva and bacteria can enter the handpiece. Consequently, the handpiece can maintain better asepsis and leak less oil and lubricant than the handpieces now in use.
Another old means used to secure a dental instrument in the handpiece is to use a tube or a slitted collet to grip the dental instrument, wherein a cam-shaped tube which surrounds the collet pushes in the fingers between the slots so that they may grip a dental tool. The disadvantages of this construction, as to cost and difficulty of manufacture, as well as difficulty in properly centering the tool in the collet and excessive wear, are self-evident.
The groove grip used in the present invention eliminates the problems caused by the prior art devices. Because of the design of the present invention, the parts of the device may be more easily machined, so that the problem with eccentricity can be obviated. There is also negligible difficulty with the breaking of any part of the present invention.
Also, the present invention can be assembled from the instrument end only. In this assembly, thrust bearings can be set in properly adjusted position, and locked; and the journal bearings are arranged to promote maximum stability against tool wobble.